1. Field of the Invention
The present invention relates to an image reader used for reading out images (and/or text) carried by a sheet member (such as an opaque paper sheet or a transparent plastic sheet). The present invention also relates to an apparatus incorporating such an image reader.
2. Description of the Related Art
Typically, an image reader of the above type includes a light source for illuminating image-carrying members, a light-sensitive detector (such as a charge-coupled device) for detecting reflection light coming from the image-carrying member, and an optical system (including a combination of mirrors and lenses) for leading the above reflection light to the light-sensitive detector.
In general, the light-sensitive detector is an elongated sensor consisting of e.g., phototransistors arranged in an array. Due to this linear arrangement, phototransistors disposed near the longitudinal ends of the detector tend to receive less light (less luminous energy) than those disposed around or at the center of the detector do. Such imbalance is undesirable and needs correction. (The correction will be called xe2x80x9cshading correctionxe2x80x9d hereinafter).
One way to provide the shading correction may be to use a light shield member arranged for partially blocking the passage of the reflection light. An example of light shield member is disclosed in Japanese Patent Application Laid-open No. 61(1986)-111058. As shown in FIG. 4 of the above application, the conventional light shield member 22 includes a downward protrusion hanging in front of the lens 7. In this arrangement, central region of the light passage is partially blocked so that intended shading correction is provided.
A problem associated with the light shield member of the above application is as follows. As shown in FIG. 4 of the above application, the conventional light shield member 22 is attached to a stationary frame 21. In accordance with the conventional arrangement, the distance between an image forming lens 7 and the light shield member 22 may vary when the lens 7 is shifted with respect to the frame 21 for adjustment of the focus of the lens 7. Such variation may unduly affect the light-shielding performance of the light shield member 22, whereby the intended shading correction will not be obtained.
It is, therefore, an object of the present invention is to provide an image reader capable of overcoming the above problem.
Another object of the present invention is to provide an apparatus in which such an image reader is advantageously incorporated.
According to a first aspect of the present invention, there is provided an image reader for an image-carrying member comprising:
a light source for illuminating the image-carrying member;
a sensor for detection of light coming from the image-carrying member along a predetermined path;
a lens movable along said path for focal adjustment; and
a shield member for partially blocking passage of said light;
wherein the lens and the shield member are identically moved while the focal adjustment of the lens is being performed.
With such an arrangement, the lens and the shield member are identically moved (meaning that the lens and the shield member keep an initial distance to each other). Thus, the intended shading correction is obtained even when the lens is shifted in position for its focal adjustment.
According to a preferred embodiment of the present invention, the image reader further comprises a lens holder for fixing the lens and a carrier member for carrying the lens holder. The carrier member is movable along said path.
The carrier member may be formed with a groove extending through the carrier member, while the image reader may further comprise a stationary guide rail fitted in the groove of the carrier member. In the assembled state, the carrier member is slidable along the guide rail.
The lens holder may comprise a cylindrical member having a curved side surface, and the carrier member may have a curved surface for supporting the lens holder.
Advantageously, the carrier member is provided with a first wall and a second wall. The first wall may include the shield member. The second wall may be shorter than the first wall.
A distance between the first wall and the second wall may be substantially equal to a length of the lens holder. In this arrangement, the lens holder is readily attached to the carrier member simply by inserting the lens holder into. a space between the first wall and the second wall.
Preferably, the carrier member, the first wall and the second wall may be formed integral to each other as a single piece.
According to a second aspect of the present invention, there is provided an image reader for an image-carrying member comprising:
a sensor for detection of light coming from the image-carrying member along a predetermined path;
a lens movable along said path for focal adjustment; and
a shield member for partially blocking passage of said light;
wherein the lens and the shield member are arranged to keep a predetermined distance to each other while the focal adjustment of the lens is being performed.
According to a third aspect of the present invention, there is provided a facsimile machine incorporating an image reader for an image-carrying member, the image reader comprising:
a light source for illuminating the image-carrying member;
a sensor for detection of light coming from the image-carrying member along a predetermined path;
a lens movable along said path for focal adjustment; and
a shield member for partially blocking passage of said light;
wherein the lens and the shield member are identically moved while the focal adjustment of the lens is being performed.
According to a fourth aspect of the present invention, there is provided a multi-function apparatus having functions of a facsimile machine, a printer, an image scanner, a photocopier, or the like, the multi-function apparatus incorporating an image reader for an image-carrying member, the image reader comprising:
a sensor for detection of light coming from the image-carrying member along a predetermined path;
a lens movable along said path for focal adjustment; and
a shield member for partially blocking passage of said light;
wherein the lens and the shield member are arranged to keep a predetermined distance to each other while the focal adjustment of the lens is being performed.
Other objects, features and advantages of the present invention will be apparent from the detailed description of the embodiment given below with reference to the accompanying drawings.